Processes for electrochemical up-cycling of plastics and systems thereof

ABSTRACT

Methods and systems for the electrochemical up-cycling of polymers. A slurry including a mixture of solid plastics flows through an electrochemical cell, which, through an applied potential, the plastics are converted into pure hydrogen, fuels, gasolines, and oxygen hydrogenated compounds that can be used for the synthesis of advanced materials and/or for easier biochemical/thermal degradation. Such methods and systems enables converting plastic waste to into fuels, chemicals, and high value products.

This application is a PCT Application claiming priority to U.S. Provisional Patent Application Ser. No. 63/040,929, filed on Jun. 18, 2020, entitled “Processes For Electrochemical Up-Cycling Of Plastics And Systems Thereof.”

TECHNICAL FIELD

The present invention relates to the field of polymer up-cycling and systems thereof, and more particularly to processes for electrochemical up-cycling of plastics and systems thereof.

BACKGROUND

Plastics are ubiquitous in modern life. They are made from synthetic carbon-based polymers—organic macromolecules made up of many repeating subunits called monomers—and are designed to be durable and resistant to degradation as well are low cost to produce. The rate of plastics production is currently higher than 400 million metric tons per year (over 8 billion metric tons produced in the past 50 years), with only 20% of used plastics mechanically recycled. [UNEP 2018]. The remainder of the billions of metric tons of plastic produced in the world has been dumped into landfills and oceans, causing serious environmental, health and economic damage.

The properties that make plastics useful, are also responsible for their difficult degradation once they are discarded as waste. Efficient technologies for revalorization of waste polymers could lead to recovering 3.5 billion barrels of oil per year ($175B at $50/barrel), opening opportunities for novel domestic manufacturing. [Celik 2019].

Chemical recycling converts polymers to molecular intermediates that can be used to make new products, creating new value chains for what is currently a waste stream. However, current deconstruction approaches either degrade the properties of the feedstock or are too energy intensive. Polymer upcycling, in contrast, aims at selectively deconstructing polymers into value-added products under mild conditions. [USDOE 2019]. However, current methods for polymer upcycling are highly energy intensive, require separations of products (which impacts process costs by ˜40-50%); and the capital costs for production when compared to the processing capacity.

Current deconstruction approaches either degrade the properties of the feedstock or methods for polymer upcycling are highly energy intensive, require separations of products, which impacts process costs by 40-50%. Current methods include thermal cracking, incineration, and disposing in landfills. Incineration recovers only about half of the energy saved by recycling, biodegradation of current plastics can take hundreds of years, and mechanical recycling—a process of melting and extruding the material—downgrades polymers, limiting their recycle rate.

Moreover, current waste management processes, consisting of mechanical recycling and incineration to recuperate energy, are only capable of handling around 40% of the plastic waste produced worldwide, while the rest is disposed of in landfills and ecosystems, posing severe threats to the environment and circular economy. [Geyer 2019]. The largest fraction of such waste is polyethylene and polypropylene, which have remarkable kinetic and thermodynamic stability. As a result, common strategies for depolymerizing polyolefins are based on high temperature pyrolysis, supercritical water, and hydrogenolysis. [Das 2017]. These approaches, however, are not compatible with the principles of delocalized chemical processing and sustainable chemical manufacturing. Successful conversion approaches will have to produce value-added, easy to transport, products with near zero waste and carbon footprint. Electrochemical depolymerization and upgrading of plastics is a promising approach for plastics upcycling as it can utilize renewable electricity to create an external potential, which can shift the system out of equilibrium. Thus, an electrochemically driven process can overcome the thermodynamic constraints that the endothermicity of the C—C bond cleavage imposes to low-temperature polymer conversion.[Möhle 2018; Rafiee 2019; Kärkäs 2018]. However, fundamental research on the mechanistic aspects of chemistry behind such process is lacking.

Therefore, modular and scalable methods that enable the production of high value products from mixtures of plastics are needed.

SUMMARY OF THE INVENTION

The present invention is directed to processes for electrochemical up-cycling of plastics and systems thereof. Polymer upcycling aims at selectively deconstructing polymers into value-added products under mild conditions. In embodiments of the present invention, the processes transform recalcitrant polymers and mixtures of plastics into high value chemicals (hydrogen, gasolines, monomers) and high value oxy-hydrogenated char that can be further processed into value products via biological and thermal processes.

The present invention targets plastic upcycling by electrochemically depolymerizing plastics and converting them into monomers and fuels and/or value-added molecules, leading to a circular economy of plastics. A slurry including a mixture of solid plastics flows through an electrochemical cell/anode, which converts into pure hydrogen, fuels, gasolines, and oxygen hydrogenated compounds that can be used for the synthesis of advanced materials and/or for easier biochemical/thermal degradation. A cell voltage is applied between the anode and the cathode of the cell. It is believed that this is the first time a cell voltage is applied to de-polymerize plastics. The present invention enables to use plastic waste to be converted into fuels, chemicals, and products of higher quality or value.

The present invention overcomes the challenge of plastic waste upcycling by using sustainable, green chemistry methods, to selectively implement electrochemical functionalization and deconstruction of polymers (such as low-density polyethylene (LDPE)) at room temperature, low applied potential such as at 1 V), and mild reaction media by low cost first row transition metals electrocatalysts.

In some embodiments, the present invention provides for the functionalization of polymers (such as LDPE) enabled by shuttle electrode/electrolyte pairs and applied electric potential via three different electrocatalysts (Ni, Cu, Fe) in the mild reaction conditions. This process includes reacting the polymer with redox species formed between two electrodes oscillating between opposing polarities in undivided electrochemical cells. One advantage of the proposed approach is that dissolution or melting of the polymer is not a prerequisite for upcycling, whereas the selection of electrolyte, applied potential, oscillation frequency, electrode composition, and operating temperature provides a unique level of control over the degree of depolymerization, functionalization, and the composition of the products.

In general, in one embodiment, the invention features a method for electrochemical up-cycling of polymers. The method includes preparing a slurry comprising a mixture of plastic particles. The method further includes flowing the slurry into an electrochemical cell. The electrochemical cell includes (A) a cathode in a cathode compartment and (B) an anode in an anode compartment. The slurry is flown through the anode compartment. The method further includes providing a medium selected from a group consisting of (i) an electrolyte (in which (A) the electrolyte is flowable though the cathode of the electrochemical cell, and (B) the electrochemical cell further includes a membrane or separator between the anode and the cathode) and (ii) protons that can be pumped from decomposition of the plastic particles in the slurry from the anode and reduced at the cathode. The method further includes providing a voltage or current between the anode and the cathode of the electrochemical cell. The method further includes oxidizing the plastic particles in the slurry to prepare a product selected from a group consisting of fuels, chemicals, oxy-hydrogenated products, and combinations thereof.

Implementations of the invention can include one or more of the following features:

The product can be selected from a group consisting of pure hydrogen, gasolines, monomers, and combinations thereof.

The product can be an oxygen hydrogenated compound that can be used for at least of one the synthesis of materials and biochemical/thermal degradation.

The slurry can be a mixture of plastics and polymers.

The slurry can be formed by grinding plastics.

The slurry can further include the electrolyte.

The particle size of the plastic particles can be in a range of about 10 microns and about 2000 microns.

The anode can include a conductive material support selected from a group consisting of Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys, graphite, nickel foam, Ti foam, aluminum, aluminum foam, and combinations thereof.

The anode can include a conductive material support selected from a group consisting of carbon, carbon fibers, and graphene.

The anode can include a catalyst that includes a metal selected from a group consisting of Ni, Fe, Co, Cr, Mo, Pt, Rh, Ru, Pd, Ir, combinations thereof, and composites of graphene metal combinations.

The loading of the catalyst can be in a range between 0.1 mg/cm² and 2 mg/cm².

The anode can include a catalyst that includes carbon material selected from a group consisting of carbon fibers, carbon paper, carbon cloth, graphene, and carbon nanotubes.

The anode can be a carbon fiber electrode that includes a Pt electrocatalyst.

The anode can be a Ni mesh electrode.

The cathode can include a conductive material support selected from a group consisting of Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys, graphite, nickel foam, Ti foam, aluminum, aluminum foam, and combination thereof.

The cathode can include a conductive material support selected from a group consisting of carbon, carbon fibers, carbon paper, carbon cloth, and graphene.

The cathode can include an electrocatalyst that includes a material selected from a group consisting of carbon, graphene, Ni, Fe, Co, Mo, Pt, Rh, Ru, Pd, Ir, and combinations thereof.

The electrochemical cell can include the electrolyte.

The electrochemical cell can include the membrane.

The membrane can include nafion or fritted glass.

The electrochemical cell can include the separator.

The separator can include polyethylene.

The electrolyte can include an acid.

The acid can be sulfuric acid or phosphoric acid.

The acid can be at a concentration in a range of 0.1 M and 9 M.

The electrolyte can include a catalytic additive.

The catalytic additive can include an additive selected from a group consisting of Fe⁺², Fe⁺³, Cr⁺², Cr⁺³, V⁺³, V⁺², and salts thereof.

The catalytic additive can be at a concentration in a range of 10 mM and 1000 mM.

The electrochemical cell can include an additive.

The electrochemical cell further include a reference electrode.

The reference electrode can include a material selected from a group consisting of Pt, Ni, Au, Ag/AgCl, Ag, and combinations thereof.

The step of oxidizing the plastic particles can occur while controlling temperature in a range between 20° C. and 180° C.

In general, in another embodiment, the invention features a system for electrochemical up-cycling of polymers. The system includes a slurry reservoir containing a slurry that includes a mixture of plastic particles. The system further includes an electrochemical cell. The electrochemical cell includes (A) a cathode in a cathode compartment and (B) an anode in an anode compartment. The electrochemical cell is operatively connected to the reservoir to provide for slurry from to flow through the anode compartment. The system further includes a medium selected from a group consisting of (i) an electrolyte (in which (A) the electrolyte is flowable though the cathode of the cell, and (B) the electrochemical cell further includes a membrane or separator between the anode and the cathode) and (ii) protons that can be pumped from decomposition of the plastic particles in the slurry from the anode and reduced at the cathode. The system further includes a cell controller that is operable to control voltage or current between the anode and the cathode of the electrochemical cell. The electrochemical cell, the medium, and the cell controller are operable for oxidizing the plastic particles in the slurry to form a product. The product is selected from a group consisting of fuels, chemicals, oxy-hydrogenated products, and combinations thereof. The system further includes one or more product reservoirs operatively connected to the electrochemical cell to receive the product.

Implementations of the invention can include one or more of the following features:

The product can be selected from a group consisting of pure hydrogen, gasolines, monomers, and combinations thereof.

The product can be an oxygen hydrogenated compound that can be used for at least of one the synthesis of materials and biochemical/thermal degradation.

The slurry can be a mixture of plastics and polymers.

The slurry can be ground plastics.

The slurry can further include the electrolyte.

The particle size of the plastic particles can be in a range of about 10 microns and about 2000 microns.

The anode can include a conductive material support selected from a group consisting of Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys, graphite, nickel foam, Ti foam, aluminum, aluminum foam, and combinations thereof.

The anode can include a conductive material support selected from a group consisting of carbon, carbon fibers, and graphene.

The anode can include a catalyst that includes a metal selected from a group consisting of Ni, Fe, Co, Cr, Mo, Pt, Rh, Ru, Pd, Ir, combinations thereof, and composites of graphene metal combinations.

The loading of the catalyst can be in a range between 0.1 mg/cm² and 2 mg/cm².

The anode can include a catalyst that includes carbon material selected from a group consisting of carbon fibers, carbon cloth, graphene, and carbon nanotubes.

The anode can be a carbon fiber electrode that includes a Pt electrocatalyst.

The anode can be a Ni mesh electrode.

The cathode can include a conductive material support selected from a group consisting of Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys, graphite, nickel foam, Ti foam, aluminum, aluminum foam, and combination thereof.

The cathode can include a conductive material support selected from a group consisting of carbon, carbon fibers, carbon paper, carbon cloth, and graphene.

The cathode can include an electrocatalyst that includes a material selected from a group consisting of carbon, graphene, Ni, Fe, Co, Mo, Pt, Rh, Ru, Pd, Ir, and combinations thereof.

The electrochemical cell can include the electrolyte.

The electrochemical cell can include the membrane.

The membrane can include nafion or fritted glass.

The electrochemical cell can include the separator.

The separator can include polyethylene.

The electrolyte can include an acid.

The acid can be sulfuric acid or phosphoric acid.

The acid can be at a concentration in a range of 0.1 M and 9 M.

The electrolyte can include a catalytic additive.

The catalytic additive can include an additive selected from a group consisting of Fe⁺², Fe⁺³, Cr⁺², Cr⁺³, V⁺³, V⁺², and salts thereof.

The catalytic additive can be at a concentration in a range of 10 mM and 1000 mM.

The electrochemical cell can include an additive.

The electrochemical cell further can include a reference electrode.

The reference electrode can include a material selected from a group consisting of Pt, Ni, Au, Ag/AgCl, Ag, and combinations thereof.

The system can further a heater and a temperature controller that is operably connected to, and operable to control, the heater. The heater and the temperature controller can be operable to control the temperature in the electrochemical cell during oxidation of the plastic particles in the slurry to form the product.

The heater and temperature control can be operable for controlling temperature in a range between 20° C. and 180° C.

The one or more product reservoirs can be selected from a group consisting of gas collectors, condensers, containers, pumps, and combinations thereof.

In general, in another embodiment, the invention features a method for electrical oxidation of a polymer. The method includes dispersing a polymer in an electrolyte including an electrolcatalyst to form a slurry. The method further includes utilizing an electrochemical cell to selectively functionalize and deconstruct the polymer in the slurry at room temperature. The electrochemical cell includes two electrodes with the slurry therebetween. The electrochemical cell is utilized by applying a low potential between the two electrodes. The low potential is modulated with a predetermined switching frequency.

Implementations of the invention can include one or more of the following features:

The electrocatalyst can include a first row transition metal.

The electrocatalyst can be selected from a group consisting of NI, Cu, Fe, and combinations thereof.

The electrochemical cell can be a bipolar single chamber packed bed electrolysis cell.

The two electrodes can be selected from a group consisting of copper, nickel, and stainless steel electrodes.

The polymer can include low-density polyethylene (LDPE).

The method can further include using an acid to adjust the pH of the electrolyte to approximately neutral.

The concentration of the polymer dispersed in the slurry can be between 10 mg to 20 mg per 1 ml of the electrolyte.

The predetermined switching frequency can be between 5 to 15 seconds.

The low potential can be between 0.5 to 1.5 V.

The selective functionalization of the polymer can be selected from a group consisting of (i) direct electrooxidation mediated by organometallic complexes, (ii) indirect electrooxidation via ionic strength modulated by potential control, (iii) direct electrooxidation led by pre-adsorbed ions, (iv) indirect oxidation via electro-Fenton, and (v) combinations thereof.

In general, in another embodiment, the invention feature a system for electrical oxidation of a polymer. The system includes a slurry including a polymer dispersed in an electrolyte comprising an electrolcatalyst. The system further includes an electrochemical cell including two electrodes with the slurry therebetween. The system further includes a cell controller that is operable to apply a low potential between the two electrodes. The low potential is modulated with a predetermined switching frequency. The application of the low potential is operable to selectively functionalize and deconstruct the polymer in the slurry at room temperature.

Implementations of the invention can include one or more of the following features:

The electrocatalyst can include a first row transition metal.

The electrocatalyst can be selected from a group consisting of NI, Cu, Fe, and combinations thereof.

The electrochemical cell can be a bipolar single chamber packed bed electrolysis cell.

The two electrodes can be selected from a group consisting of copper, nickel, and stainless steel electrodes.

The polymer can include low-density polyethylene (LDPE).

The method can further include using an acid to adjust the pH of the electrolyte to approximately neutral.

The concentration of the polymer dispersed in the slurry can be between 10 mg to 20 mg per 1 ml of the electrolyte.

The predetermined switching frequency can be between 5 to 15 seconds.

The low potential can be between 0.5 to 1.5 V.

The selective functionalization of the polymer can be selected from a group consisting of (i) direct electrooxidation mediated by organometallic complexes, (ii) indirect electrooxidation via ionic strength modulated by potential control, (iii) direct electrooxidation led by pre-adsorbed ions, (iv) indirect oxidation via electro-Fenton, and (v) combinations thereof.

DESCRIPTION OF DRAWINGS

FIG. 1 is schematic diagram of a process for electrochemical depolymerization and upcycling of plastics of the present invention.

FIGS. 2A-2B are photographs of (FIG. 2A) carbon fiber electrodes with Pt electrocatalysts, and (FIG. 2B) a Ni mesh electrode that can be used in embodiments of the present invention.

FIG. 3 is a schematic of a rig for the electrolysis of polymers in the present invention.

FIG. 4 is a graph showing current density at constant voltage (1.17 V) for Pt and Ni electrodes.

FIG. 5 is a graph showing FTIR spectrum of electrooxidized LDPE at different conditions.

FIG. 6 is a graph showing GC/MS data of organic products dissolved in the electrolyte after the electrolysis with: (plot 601) Pt electrode with 1 M H₂SO₄ at 95° C., (plot 602) Pt electrode with 4 M H₂SO₄ at 105° C., (plot 603) Ni electrode with 1 M H₂SO₄ at 90° C.

FIG. 7A is an illustration of a packed bed electrolysis cell for electrochemical upcycling of LDPE.

FIG. 7B is a graph showing the switch of polarity utilized for the packed bed electrolysis cell shown in FIG. 7A.

FIG. 8 are graphs showing the FTIR spectra of LDPE samples in the region of 800 cm⁻¹ to 1400 cm⁻¹ for pristine, after 2 hours chemical treatment in different electrolyte solutions at room temperature, and after 2 hours electrolysis at room temperature.

FIG. 9 are graphs showing the FTIR spectra of LDPE samples in the region of 1500 cm⁻¹ to 2000 cm⁻¹ for pristine, after 2 hours chemical treatment in different electrolyte solutions at room temperature, and after 2 hours electrolysis at room temperature.

FIG. 10 are graphs showing the FTIR spectra of LDPE samples in the region of 3000 cm⁻¹ to 4000 cm⁻¹ for pristine, after 2 hours chemical treatment in different electrolyte solutions at room temperature, and after 2 hours electrolysis at room temperature.

FIGS. 11A-11D are schematics for direct electrooxidation mediated by organometallic complexes proposed oxidation mechanism.

FIG. 12 is a schematic for indirect electrooxidation via ionic strength modulated by potential control.

FIG. 13 show direct electrochemical oxidation mechanisms of polyolefins via water discharge reaction.

FIG. 14 is a schematic for indirect oxidation radical mechanism (electro-Fenton chemistry).

FIG. 15 shows mechanisms for Fenton chemistry initiated by hydrogen and oxygen.

DETAILED DESCRIPTION

The present invention is related to polymer up-cycling and systems thereof, and more particularly to processes for electrochemical up-cycling of plastics and systems thereof. The processes of the present invention transform recalcitrant polymers and mixtures of plastics into high value chemicals (hydrogen, gasolines, monomers) and high value oxy-hydrogenated char that can be further processed into value products via biological and thermal processes.

FIG. 1 is schematic diagram of a process for electrochemical depolymerization and upcycling of plastics of the present invention. Such decarbonization leads to the production of H₂ and other valuable chemicals, as well as products for further processing as advanced materials.

In general, the process shown in FIG. 1 involves the following steps:

-   -   (a) An electrochemical cell 101 containing an anode, cathode,         and a membrane or separator are integrated, such as shown in         FIG. 1 .     -   (b) A slurry 102 prepared by a mixture of grinded plastics and         electrolyte is flown through the anode compartment of the         electrochemical cell 101.     -   (c) An electrolyte is flown through the cathode of the cell (if         using a membrane), or protons are pumped from the decomposition         of the components from the anode and reduced at the cathode.     -   (d) A cell voltage 103 is applied between the anode and cathode         of the electrochemical cell 101.     -   (e) The plastic slurry 102 is oxidized producing high value         chemicals such as gasolines, monomers, methane, high value         chemicals, and a high value char. A general reaction is depicted         in Eq. (1).

2n˜(C)+2H₂O→2n(C—OH)+2H⁺+2e ⁻  (1)

-   -   (f) Pure hydrogen is produced at the cathode of the cell         according to the reaction Eq. (2).

2H⁺+2e ⁻→H₂  (2)

The most recalcitrant plastics—such as polyethylene, polypropylene, and polyvinyl chloride—lack oxygen groups, which makes these polymers highly stable but difficult to recycle. The presence of oxy-hydrogenated bonds depicted in Eq. (1) makes the char left from the process highly recyclable and an important feedstock for the synthesis of advanced materials such as graphene, carbon nanotubes, monomers, etc.

The process of the present invention enables the low temperature hydrolysis of plastics producing lower molecular weight macromolecules, hydrogen, fuels and chemicals of value. Other transformational advantages include: (1) selectivity for the removal/oxidation of additives included in the product (most plastics contain additives that create complexity during their recycling); (2) direct application of electrons for breaking bonds in the chain of the polymeric structure; (3) tolerance to hybrid mixtures of plastics, which minimizes separation of plastic wastes; (4) implementation of renewable sources of energy (solar, wind); (5) co-generation of high value products such as H₂, chemicals, fuels; (6) and modularity (which makes the process eligible for distributed processing of plastics into high value chemicals).

It is believe that this is the first time a cell voltage is applied to de-polymerize plastics. It is further believed that the electrochemical up-cycling of solid plastic slurries have not been reported. Hori 2020 reported a study on the use of plastic waste as a feedstock for fuel cell applications. Hori et al. focused on the implementation of polymers that can be solubilized in acid electrolytes at relatively high temperatures (˜200° C.) such as polyurethane, nylon, and vinylon. They demonstrated the conversion of the different polymers into electricity using phosphoric acid as electrolyte and platinum electrocatalyst supported in mesoporous carbon. When the polymer was dissolved in an electrolyte at high temperature, it was typically decomposed, acting as an organic chemical in the fuel cell. In addition, the type of polymers used dissolve because they contain oxygen groups in the change. Hori et al. reported the production of carbon dioxide at the anode with traces of methane. The approach reported by Hori et al. worked only for solubilized polymers and not for insoluble and/or solid slurries.

Electrochemical Cell

The electrochemical cell of the present invention can include (a) an anode, (b) a cathode, (c) a membrane or separator, and (d) electrolyte or additive. In some embodiments, the electrochemical cell may further include a reference electrode.

Anodes

Examples of anodes utilized in embodiments of the present invention can include:

Anodes constituted by a conductive material support, e.g., Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys (such as Hastelloy metal), graphite, nickel foam, Ti foam, aluminum, aluminum foam, etc. Generally, the anodes can be formed from any conductive material while being resistance to corrosion based on the electrolyte, cell voltage, and temperature of the system.

Other supports for the anodes include carbon, carbon fibers, carbon paper, carbon cloth, and graphene.

The catalyst for the anode can include metals such as Ni, Fe, Co, Cr, Mo, Pt, Rh, Ru, Pd, Ir, and combinations thereof, and composites of graphene metal combinations. The loadings can be in the range of 0.1 mg/cm² and 2 mg/cm².

In some embodiments, the catalyst is a carbon material, such as carbon fibers, carbon paper, carbon cloth, graphene, and carbon nanotubes.

Cathode

Examples of cathodes utilized in embodiments of the present invention can include:

Cathodes constituted by a conductive material support, e.g., nickel gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys (such as Hastelloy metal), graphite, carbon paper, carbon cloth, graphene, etc. Generally, the cathodes can formed from any conductive material while being resistance to corrosion based on the electrolyte, cell voltage and temperature of the system.

Electrocatalyst of the cathode can be made of materials including, carbon, graphene, Ni, Fe, Co, Mo, Pt, Rh, Ru, Pd, Ir, and combinations thereof.

Membrane and/or Separator

The electrochemical cell of the present invention can contain a membrane, such as nafion, fritted glass, etc., and/or separators, e.g., polyethylene.

Electrolyte and Additives

Electrolytes/additives utilized in the present invention can be acid including strong and weak acids, e.g., sulfuric acid, phosphoric acid, etc. The concentrations can be in the range of 0.1 M and 9 M (depending on the electrolyte and their solubility in the solvent).

The electrolyte can contain catalytic additives such as Fe⁺², Fe⁺³, Cr⁺², Cr⁺³, V⁺³, V⁺² etc. The concentrations of the salt/additives can be in the range of 10 mM and 1000 mM.

Reference Electrode

In some embodiments of the present invention, the potential can be applied versus a reference or pseudo reference electrode. For example, the reference electrode can be made of a material such as Pt, Ni, Au, Ag/AgCl, Ag, and combinations thereof.

Process for Electrochemical UP-Cycling

Generally, the process of the present invention includes:

-   -   (a) The slurry 102 is flowed through the anode of the cell 101;     -   (b) The electrolyte can be recirculated through the cathode of         the cell 101;     -   (c) Cell voltage 103 is applied between the anode and the         cathode of the cell. In some embodiments, alternatively, current         is applied instead of a voltage; and     -   (d) Temperature is controlled during the process.

This electrochemical depolarization and upcycling of plastics process (such as shown in FIG. 1 ) can convert plastic waste to into fuels (such as H₂) 104, chemicals 105, and products of higher quality or value (such as oxy-hydrogenated by-products for thermal post processing 106).

Slurry

The slurry 102 can be prepared from a mixture of plastics and/or polymers.

In some embodiments, the particle size of plastics can be in the range of about 10 microns and about 2000 microns.

In some embodiments, the slurry is a mixture of plastics and electrolyte and/or additives.

Cell Voltage

Generally, cell voltage 103 of up to 1.5V can be applied, depending on the type of electrolyte use and the temperature. A goal is to prevent water oxidation at the anode of the cell 101. Oxidation potential is a function of the electrolyte and temperature used.

Temperature

Generally, the temperature is controlled to be within the range of 20° C. and 180° C.

Example Processes Electrochemical Cell and Rig Examples

Examples of electrolysis methods were performed using low density polyethylene (LDPE) powder with 500 micron particles size (supplied by Alfa Aesar, ACS #9002-88-4), with a melting point of 190° C. and density of 0.9220 g/ml. [ThermoFisher 2020].

A slurry dispersion was created by mixing the powder plastic with electrolyte, in this case, sulfuric acid. The dispersion of the slurry was affected by the velocity. An electrochemical cell 303 and rig 300 for the electrolysis were built as shown in FIGS. 2A-2B and 3 .

Two anode electrode configurations were tested, shown in FIGS. 2A-2B, respectively, with FIG. 2A showing a carbon fiber electrode with Pt electrocatalysts and FIG. 2B showing a Ni mesh electrode. Nickel mesh, and carbon fibers (support, BASF polyacrylonitrile-PAN-carbon fiber from Celion G30-500, 7 micron diameter) spray coated with Pt (using nafion as the binder) nanocatalyst (loading of 1 mg/cm²) supported on Vulcan XC-72R prepared by the polyol method through ethylene glycol reduction reaction. [Li 2017].

In all the cases, the cathode was prepared by spray coating of Pt on Vulcan/nafion ink on carbon fibers with a loading of 1 mg/cm². Nafion 117 was used to separate the anodic and cathodic compartments of the electrolysis cell 303 (shown in FIG. 3 ). Both Ni and Pt electrocatalysts represent a spectrum of possibilities for the electrolysis of polyethylene (PE).

Schematic of the rig 300 is shown in FIG. 3 . Rig 300 includes (a) slurry/plastic dispersion container 301 (which contains the slurry/plastic dispersion), (b) connectors 302 to voltage controller, (c) electrolysis cell 303, (d) stirring plates 304, (e) temperature heaters and controllers 305, (f) gas collectors 306, (g) condensers 307, and (h) pumps 308. Rig 300 can be used to enable control of temperature, applying cell voltage (or current), and quantification and collection of gases produced (by water displacement).

Utilizing rig 300, electrolysis was performed using sulfuric acid as electrolyte at 90-105° C. at a constant cell voltage of 1.17 V (to prevent water electrolysis and oxidation of the carbon electrode support). Electrolysis with the Pt electrode (shown in FIG. 2A) included 40 mM of Fe²⁺+/Fe³⁺ to start the reaction. The electrochemical response of the system is shown in FIG. 4 . Plots 401-402 are, respectively, the Pt with sulfuric acid and iron baseline and Ni baseline. Plots 403-404 are, respectively, the Pt with polyethylene (PE) and Ni with PE.

In all cases when PE slurry was present, oxidation currents were observed (i.e., electrochemical oxidation of the PE was observed in both Pt and Ni based electrodes). For the Ni electrode, no significant corrosion was observed with the blank electrolyte, and the current density increased significantly when PE was added into the solution. At that point, some dissolution of the Ni electrode was observed. The current dropped abruptly due to pump dis-control, which was later fixed. For the Pt electrode, the change observed was slightly higher than for the oxidation of Fe²⁺, indicating some oxidation of the LDPE. In both cases, hydrogen gas was produced at the cathodic compartment of the cell, demonstrating reaction (2).

Ex-situ Fourier Transform Infrared (FTIR) was conducted to evaluate the oxidation of the polymer after electrolysis, which results are shown in FIG. 5 (showing FTIR spectrum of electrooxidized LDPE at different conditions, with presence of carboxylic groups and OH are observed after electrolysis). Plots 501-504 are, respectively, the plots for (501) raw PE, (502) Ni electrode, (503) Pt electrode (95° C., 1 M H₂SO₄), and (504) Pt electrode (105° C., 4 M H₂SO₄). FTIR spectra were collected in the wave numbers of 500-4000 cm⁻¹.

The electrolyzed product from the Ni electrode shows significant oxidation and the presence of oxygen-hydrogenated groups: OH-stretching due to hydroperoxide, or alcohol functional groups (3400 cm⁻¹) (shown in box 505), C═O bonds indicate carboxylic, aldehydes, ketones, or esters functional groups (1700 cm⁻¹) (shown in box 506), C—O bonds at 1200 cm⁻¹ are an indication of ether functional groups (shown in box 507), OC—O—CO vibrations at 1050 cm⁻¹ are an indication of anhydride groups (shown in box 508), and C═C bending at 900 cm⁻¹ can be an indication of alkenes functional groups (shown in box 509). The significant oxidation and the presence of —OH groups confirm the electrochemical oxidation of PE. For the Pt electrode, mild oxidations of PE are observed at 95° C. with 1 M H₂SO₄ (plot 503) but much higher oxidation is observed at 105° C. with 4 M H₂SO₄ (plot 504).

Analysis of the products in the electrolyte was performed via combined gas chromatography/mass spectrometry, in which the organic compounds were extracted on dichloromethane from the electrolyte. Plots 601-603 are, respectively, plots of GC/MS data of organic products dissolved in the electrolyte after the electrolysis with: (601) Pt electrode with 1 M H₂SO₄ at 95° C., (602) Pt electrode with 4 M H₂SO₄ at 105° C., and (603) Ni electrode with 1 M H₂SO₄ at 90° C. Peaks of plots 601-603 are for (a) peaks 606 for benzene (C₆H₆), (b) peaks 607 for heptane (C₆H₁₆), (c) peaks 608 for octane (C₈H₁₈), (d) peaks 612 for dodecane (C₁₂H₂₆), (e) peaks 614 for tetradecane (C₁₄H₃₀), (f) peaks 615 for pentadecane (C₁₅H₃₂), (g) peaks 618 for octadecane (C₁₈H₃₈), (h) peaks 620 for eicosane (C₂₀H₄₂), and (e) peaks 622 for docosane (C₂₂H₄₆).

The results shown in FIG. 6 confirm the oxidation of LDPE into smaller chain hydrocarbons and gasoline type byproducts for both the Ni and Pt electrodes. Rheological tests performed in the electrolyzed LDPE with the Ni electrode indicate a 35% decrease in the viscosity, which is associated with a decrease in the molecular weight in the polymer.

Bipolar Single Chamber Packed Bed Electrochemical Cell Examples

Further examples were performed using low-density polyethylene (LDPE) powder with 500-micrometer particle size (supplied by Alfa Aesar) in a bipolar single chamber packed bed electrolysis cell designed to maintain the contact between the polymer, the electrolyte, and the electrodes, as shown in FIG. 7A. In FIG. 7A, the electrodes geometric area was 4 cm². LDPE 701/electrolyte 702 was held in contact with electrodes 703-704. The image of LDPE 701 in NiSO₄ electrolyte is a photograph in FIG. 7A.) The electrodes geometric area was 4 cm². LDPE 701/electrolyte 702 was held in contact with electrodes 703-704. The image of LDPE 701 in NiSO₄ electrolyte in FIG. 7A is a photograph.

LDPE 701 was dispersed in the electrolyte 702 at a concentration of 15 mg LDPE per mL of electrolyte. The cell included identical metal electrode couples 703-704, i.e., copper (0.01 in. thick, 99.9% metals basis, supplied by Alfa Aesar), nickel (0.01 in. thick, 99.9% metals basis, supplied by Alfa Aesar), and 304 stainless steel (SS) (0.03 in. thick, supplied McMaster-Carr) foils, and operated at 25° C., with the applied cell voltage modulated by potentiostat 705 between ±1V having a polarity switching frequency of 10 seconds (as shown in FIG. 7B). Electrolysis time was kept at 2 hours.

Electrolytes consisted of 1M CuSO₄, 1M NiSO₄, and 1M FeSO₄/Fe₂(SO4)₃ (all analytical grade, purchased from Fisher Chemicals) for the Cu, Ni, and SS electrode couples, respectively. The pH of the electrolyte was adjusted to zero using sulfuric acid (analytical grade, purchased from Fisher Chemicals). All the materials used as received and these examples have been performed without applying potential to study the chemical effect of electrolytes on the oxidation of LDPE. The average current densities for Cu, Ni, and SS electrodes were 120, 10.5, and 2.7 (mA/cm²), respectively.

At the operating cell potential, copper dissolution and deposition were observed (1% wt. lost per hour). In the case of nickel, dissolution of Ni and hydrogen evolution were observed (3.75% wt. lost per hour). No weight loss was observed in the SS electrode as the applied cell potential was not enough to trigger dissolution of the alloy.

After electrolysis, the LDPE particles were removed from the electrolyte by vacuum filtration, properly rinsed to remove residual electrolyte, and dried in a vacuum oven at 40° C. for 18 hours. To evaluate the oxidation of the polymer after electrolysis, Fourier Transform Infrared (FTIR) was conducted on Bruker Optics Vertex 70 spectrometer (256 scans, resolution of 2 cm⁻¹) equipped with a 45° single reflection Bruker Optics Platinum A225 attenuated total reflection (ATR) unit having diamond crystal in the range of 400-4000 cm⁻¹ at room temperature.

The penetration depth into the sample is on the order of 0.5 to 2 m. See FIGS. 8-10 . FIG. 8 shows the FTIR spectra 801-803 of LDPE samples in the region of 800 cm⁻¹ to 1400 cm⁻¹ for pristine (bottom spectra), after 2 hours chemical treatment in different electrolyte solutions at room temperature (middle spectra), and after 2 hours electrolysis at room temperature (top spectra), having ±1V cell potential in different electrodes and electrolytes for Ni electrodes/Ni salt solution (spectra 801), Cu electrodes/Cu salt solution (spectra 802), and SS electrodes/Fe salt solution (spectra 803). FIG. 9 shows the FTIR spectra 901-903 of LDPE samples in the region of 1500 cm⁻¹ to 2000 cm⁻¹ for pristine (bottom spectra), after 2 hours chemical treatment in different electrolyte solutions at room temperature (middle spectra), and after 2 hours electrolysis at room temperature (top spectra), having ±1V cell potential in different electrodes and electrolytes for Ni electrodes/Ni salt solution (spectra 901), Cu electrodes/Cu salt solution (spectra 902), and SS electrodes/Fe salt solution (spectra 903). FIG. 10 shows the FTIR spectra 1001-1003 of LDPE samples in the region of 3000 cm⁻¹ to 4000 cm⁻¹ for pristine (bottom spectra), after 2 hours chemical treatment in different electrolyte solutions at room temperature (middle spectra), and after 2 hours electrolysis at room temperature (top spectra), having ±1V cell potential in different electrodes and electrolytes for Ni electrodes/Ni salt solution (spectra 1001), Cu electrodes/Cu salt solution (spectra 1002), and SS electrodes/Fe salt solution (spectra 1003).

FTIR spectra show bands in the regions 1000-1250, 1650-1850, and 3200-3600 cm⁻¹, which are attributed to oxygen-containing functional groups such as C—O, C═O, and O—H, respectively. [Hamzah 2018; Rocha 2009]. Results demonstrate that the functionalization of LDPE is affected by applied potential, electrocatalysts and electrolyte. A detailed description of the FTIR spectra is divided into three regions: (1) C—O and C═C, (2) C═O and C═C, and (3) O—H to facilitate data presentation.

C—O and C═C region: FIG. 8 shows the effect of electrocatalyst (from spectra 801-803) and the effect of applied cell potential (from bottom to top) in the electrooxidation of LDPE. Two small vibrational absorption bands at 890 cm⁻¹ and 1080 cm⁻¹ were observed for the pristine LDPE, which were attributed to the vinylidene (C═C) and the C—O bonds mostly in the form of alcohol (C—OH) or peroxide (R—O—OH) groups. These groups are associated with the LDPE preparation methods and presence of additives in the sample (e.g., primary, and secondary antioxidants). [Chabira 2012; Ruvolo-Filho 2013]. Chemical treatment of LDPE just by electrolyte solutions shows no change in the vinylidene (890 cm⁻¹) peak while a small increase in the intensity of peaks corresponding to the alcoholic/peroxide (1080 cm⁻¹) groups [Źenkiewicz 2003] was observed.

Previous researchers have suggested that electrolytes can incorporate oxygen bonds to the polymer by the adsorption of complexes of transition metal ions at the polymer surface. [Allara 1976; Robertson 2014]. Results of these embodiments showed that LDPE samples treated electrochemically by Cu and Ni electrodes show a higher degree of oxidation as suggested by the appearance of new vibrational bands around 1150 cm⁻¹ and 1230 cm⁻¹, which was attributed to ether and ester groups. [Martinez-Colunga 2020; Tofa 2019]. The Cu electrode showed the best capability to oxidize LDPE because it not only conducted to the generation of new ether and ester vibrational absorption bands, but also led peaks corresponding to the vinylidene and the alcoholic groups get sharper and broader after electrolysis.

Meanwhile, for the SS electrode, compared to the chemical exposure, applying potential only caused a slight decrease in the alcoholic peak and a slight increase for the vinylidene peaks, suggesting that electrolysis provided energy for the creation of iron/polymer complexes leading to the formation of C═C bonds.

C═O, C═C region: FIG. 9 shows FTIR spectrum (spectra 901-903) over the region 1500 cm⁻¹ to 1850 cm⁻¹ is divided into three sub-regions: (i) 1500 cm⁻¹ to 1600 cm⁻¹, (ii) 1600 cm⁻¹ to 1650 cm⁻¹, and (iii) 1650 cm⁻¹ to 1850 cm⁻¹, which are ascribed to the carboxylate salts (COO—), C═C, and C═O functional groups, respectively. [Hamzah 2018; Lens 1997; Sibeko 2014; Yagoubi 2015]. For the pristine LDPE, there was only a peak centered at 1720 cm⁻¹, which indicated the presence of carbonyl species (ketone, carboxylic acid, ester, aldehyde, anhydride), indicating the presence of additives. [Yagoubi 2015]. The formation of carbonyl species was a result of the decomposition of hydroperoxide, ether, or alcohol groups. Accordingly, the formation of carbonyl species led to chain scission, formation of C═C bond, and finally led to decreasing the average molecular weight of the polymer (degradation). [Hamzah 2018; Chabira 2012; Yagoubi 2015; Wang 2009]. Electrochemically treated LDPE spectra, except for SS electrode, show considerable changes for the carbonyl peak, centered at 1720 cm⁻¹, while chemical exposure did not impact on the polymer. Among the three electrocatalysts, the Cu electrode showed a higher capability to lead to the introduction of carbonyl species into the polymer chain, followed by Ni and SS electrodes. C═C peak centered at 1640 cm⁻¹ appeared after electrolysis of LDPE in the three electrodes. The appearance of the peak centered at 1550 cm⁻¹ shoed the formation of carboxylate functional groups after electrolysis.

Hydroxyl (O—H) groups were formed by oxidative degradation of polymers which contain alkyl chains, such as polyolefins. [Sugiura 2000]. A broad peak from 3200 cm⁻¹ to 3550 cm⁻¹ suggested the presence of bonded OH including alcohol groups or hydroperoxides. [Rocha 2009; Abusrafa 2019]. Treatment of samples caused appearance of non-bonded or free hydroxyl groups. [Moore 2008; Quezado 1984; Liu 2013]. Peaks related to these OH groups appeared at the higher wavenumbers (more than 3600 cm⁻¹), and compared to the bonded OH, the peaks were sharper.

Surface entrapped water was one of the main sources of non-bonded OH. However, there was a possibility for the appearance of a peaks between 3700 cm⁻¹ to 3900 cm⁻¹ related to the OH bond in metal hydroxide (M-OH) compounds [Gulmine 2002; Hadjiivanov 2014; Song 2013]. According to the results, see FIG. 10 (specta 1001-1003), pristine LDPE showed a shallow broad peak in the bonded OH region (3200 cm⁻¹ to 3550 cm⁻¹) and a small peak around 3600 cm⁻¹, originating from additives and adsorbed water on the surface of polymer [Gulmine 2002], respectively. Compared to the pristine LDPE, chemically treated samples showed a stronger broad peak in the region of 3200 cm⁻¹ to 3550 cm⁻¹, which can indicate that chemical exposure to the electrolyte has the capability to add hydroperoxide or alcohol groups (primitive oxidation).

Consequently, generation or growth of the peaks at region 3600 cm⁻¹ to 3900 cm⁻¹ showed a higher number of non-bonded OH (or metal hydroxide OH) for the chemically treated samples. It is believed that the residual transitional metal ions (as a catalyst) which were already adsorbed on the polymer surface during the chemical treatment of LDPE are not stable and they turn to the metal hydroxide form. These surface metal hydroxide compounds can facilitate the adsorption of water molecules leading to the appearance of more sharp peaks between 3600 cm⁻¹ and 3900 cm⁻¹.

Except for the SS electrode, electrochemical treatment of LDPE caused vanishing of the broad peak between 3200 cm⁻¹ and 3550 cm⁻¹, which already existed for the chemically treated samples. Observation of this phenomena can show that electrolysis can provide energy for the hydroperoxide, alcohol, and non-reacted residual catalysts on the surface of the polymer to decompose them to other forms of oxygen functional groups like ether, ester, carboxyl, ketone, aldehyde, anhydride (advanced oxidation).

Based on the FTIR spectra from FIGS. 8-10 , and the observations from the literature, it is believed that the electrochemical functionalization of LDPE can occur via four different oxidation mechanisms (1) direct electrooxidation mediated by organometallic complexes, (2) indirect electrooxidation via ionic strength modulated by potential control, (3) direct electrooxidation led by pre-adsorbed ions, and (4) indirect oxidation via electro-Fenton.

Direct Electrooxidation Mediated by Organometallic Complexes: Brewis et al. demonstrated the electrochemical functionalization of polymers implementing a strong oxidant acid such as nitric acid at high concentration (3.5 M). [Brewis 2000]. The authors of Brewis 2000 observed direct oxidation of the polymer with the electrode, leading to oxygen containing groups in the backbone of the polymer. [Brewis 2000]. In embodiments of the present invention, sulfuric acid, which is a less strong oxidant than nitric acid, was used at much lower concentrations than the nitric acid reported in the literature. The fact that the presence of a week and diluted acid was still capable of providing polymer functionalization was surprising and promising and has not previously been reported in the literature.

Ionic species in the electrolyte can adsorb on the surface of the polymer and make an interaction because of their polarity. [Allara 1976; Robertson 2014]. The adsorption of such ion complex compounds on LDPE was observed in the FTIR results. Therefore, a mechanism similar to the electrochemical oxidation of complex solid fuels as proposed by Jin and Botte [Jin 2010] can be believed for polyolefins as shown in FIG. 11A-11D.

FIGS. 11A-11D are schematics for direct electrooxidation mediated by organometallic complexes proposed oxidation mechanism, namely for: (a) FIG. 11A—ion interaction/connecting bridge; (b) FIG. 11B—bridge formation with electrode polymer/ion/water molecule; (c) FIG. 11C—preferential interaction of ion with electrode lead to ion reduction/polymer oxidation; and (d) FIG. 11D—ion oxidation/process continuous.

Organometallic complexes (metal ion/water) can adsorb on the polyolefins, interact with the electrocatalysts (bridge), in turn, the cation was reduced, and the polymer oxidized (with OH integration in the polymer chain). Due to the interaction with the electrocatalyst, the reduced cation was oxidized and returned to the polymer chain to continue oxidation. The believed mechanism included the complex reaction between polymer particles and transition metal ions on the surface of the electrode and does not require the melting or dissolution of the polymer. Such mechanism can be affected by the particle size of the polyolefins, the contact of the particles with the electrocatalyst, the electrocatalyst composition, and the ionic salts implemented. Cu ions showed more tendency to make a complex with polymers followed by Ni and Fe ions. [Masoud 2015]. The believed mechanism can explain the observation that the Cu electrode was more effective towards the oxidation of LDPE due to the formation of the complex with the polymer, not observed in the SS electrodes.

Indirect electrooxidation via ionic strength modulated by potential control: Mediated Electrochemical Oxidation (MEO) of polymers have been reported implementing strong oxidizer ions (AgNO⁺³) and acids (nitric acid) at high concentration. [Brewis 2000]. A mechanism based on MEO can be hypothesized for polyolefins and presented in FIG. 12 . In the MEO process, a metal ion in an acid medium is oxidized from its lower oxidation state to a higher oxidation state and this oxidized species triggers C—C/C—H bond cleavage and gets reduced, depending on the complexity of the reactant intermediate chemicals are produced. In the process, metal ion is not consumed in the reaction and acts as a mediator. [Balaji 2007]. MEO was originally established for dissolution of difficult to dissolve forms of plutonium oxide [Chiba 1994], but later was found to be effective for oxidizing many organic materials such as polyolefins. [Brewis 2000].

In the MEO approach, the oxidizer strength of the ions can be important, the oxidizer strengths increase according to Ni⁺²>Cu⁺²>Fe⁺³, which can explain why LDPE was oxidized to a higher extent when Ni⁺² and Cu⁺² were present in the electrode. The current density in the Cu electrochemical cell as higher than for the Ni (10×) and SS electrodes (>40×), therefore the transport and distribution of the ionic charges in the electrolyte is stronger, which can lead to higher oxidation of the polymer. Such a mechanism can be controlled by the strength of the electrolyte, applied potential and frequency of oscillation, type of mediator and electrolyte, current density at the electrodes (affecting charge distribution), and temperature. [Chiba 1994].

Direct electrooxidation led by pre-adsorbed ions: Direct electrochemical oxidation of organic compounds at potentials below that required for O₂ evolution have been reported. [Treimer 2001]. The process is initiated by the hydroxyl radicals (·OH) that are generated on the electrocatalyst by the anodic water discharge reaction (WDR). A mechanism for the depolymerization of polyolefins based on WDR is shown in FIG. 13 (reactions 1301-1304). “S[ ]” represents surface sites for adsorption of OH species, “R” is the reactant (e.g., polyolefin), “S′[ ]” represents sites that maybe different to S[ ], and “S′[R]” represents adsorption of reactant, in the case of the polymer, could be enabled by complex cations adsorption on the polymer with preliminary evidence observed in the FTIR and reported in the literature. [Allara 1976; Robertson 2014].

It is believed that the carbon groups in the polyolefins were activated through interaction with metal atoms within the surface lattice followed by OH transfer, leading to depolymerization and functionalization. In embodiments of the present invention, Ni, Cu, and SS electrodes could enable the WDR. Such a mechanism can be affected by the electrocatalyst composition, the oxidation state of the metal catalyst in the electrode support, the contact of the polymer with the electrocatalyst and the particle size of the polymer.

Indirect Oxidation Radical Mechanism (electro-Fenton chemistry): In electro-Fenton chemistry hydrogen peroxide in the presence of transition metal ions can decompose to hydroxyl radicals (·OH) which are highly reactive. [Chumakov 2016]. This mighty oxidizer easily reacted with the polymer chain and caused formation of hydroperoxide functional groups. Subsequently, non-stable hydroperoxide functional groups decomposed to the other forms of oxygen functional groups like ether, ester, carboxyl, ketone, aldehyde, anhydride. [Brillas 2009]. It is believed that the electric potential triggers radical chemistry analogous to Fenton processes. Such radicals can, in turn, promote oxidative C—C bond cleavage. As shown in FIG. 14 , in a typical electro-Fenton process water is oxidized at an anodic site to oxygen, which is subsequently reduced to H₂O₂ (H₂O₂ production 1401). In parallel, electroactive molecular species is formed upon reduction at the cathode. The encounter of H₂O₂ and a Fenton-active species produces the species that initiate an oxidative bond cleavage in the polyolefins (polymer oxidation 1402). The cations that enable the Fenton cycle are likely produced by partial dissolution of the metal electrodes in acidic conditions (·OH production 1403).

In embodiments of the present invention results, the cell potential was maintained at 1V, therefore, oxygen evolution was not thermodynamically feasible. However, oxygen could have been dissolved in the electrolyte as the processes of the embodiments were performed in an open cell (see FIG. 7 ). Both Cu and Ni oxidation states reacted with H₂O₂ and produced hydroxyl radicals. [Chumakov 2016; Torreilles 1990; Zhong 2014]. Additionally, Cu⁺² complexes with organic degradation intermediates (organic acids) are easily decomposed by hydroxyl radicals, whereas the corresponding Fe⁺³ complexes are highly stable. [Bokare 2014]. It is believe that this is one of the reasons for less effectiveness of SS electrode compared to the copper electrode in oxidation of LDPE. The radical Fenton chemistry of the present invention has been proven successful in depolymerizing plastic into short chain commodity chemicals albeit with multiple reaction steps and with external oxidants. [Chow 2016].

The Fenton chemistry is also initiated by the presence of adsorbed H when hydrogen is produced as shown in FIG. 15 (reactions 1501-1505), where “M” represents the oxidation cations. The Fenton chemistry was affected by the presence of oxygen, the composition of the electrocatalyst, the applied overpotential and the frequency of oxidation, and the oxidizing strength of the cations.

Extended carbon structures, like LDPE (one of the major plastic waste), can be functionalized, oxidized, and upcycled to the value-added chemicals by applying current when they are suspended in solutions containing transition metal salts. Embodiments of the present invention show that polyethylene reacted with low, oscillating, applied electric potentials (in the order of 1.0 V) at room temperature. Upon electrochemical processing, new functional groups appear, and the concentration of others increased as a function of applied potential and electrocatalyst. Cu electrocatalyst showed the highest oxidation of LDPE when compared to Ni and SS.

Uses

The present invention technology targets plastic upcycling by electrochemically depolymerizing plastics and converting them into monomers and fuels and/or value-added molecules, leading to a circular economy of plastics. A slurry that includes a mixture of solid plastics flows through an electrochemical cell/anode, which converts into pure hydrogen, fuels, gasolines, and oxygen hydrogenated compounds that can be used for the synthesis of advanced materials and/or for easier biochemical/thermal degradation. A cell voltage is applied between the anode and the cathode of the cell; this is the first time a cell voltage is applied to de-polymerize plastics. The present invention enables to use plastic waste to be converted into fuels, chemicals, and products of higher quality or value.

The benefits of the present invention include renewable energy, plastic degradation, and value-added products. Applications of the present invention include recycling, renewable energy, clean energy, and waste management.

Before the present invention, the most commonly available chemical upcycling methods use thermal cracking processes, which cannot be performed at large scale due to being energy and economy inefficient. The electrochemical innovation described here is modular and is compatible with renewable energy.

While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. The scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.

The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.

Amounts and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of approximately 1 to approximately 4.5 should be interpreted to include not only the explicitly recited limits of 1 to approximately 4.5, but also to include individual numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than approximately 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.

Following long-standing patent law convention, the terms “a” and “an” mean “one or more” when used in this application, including the claims.

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

As used herein, the term “about” and “substantially” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments±1%, in some embodiments±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

As used herein, the term “and/or” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and/or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D.

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1. A method for electrochemical up-cycling of polymers, wherein the method comprises: (a) preparing a slurry comprising a mixture of plastic particles; (b) flowing the slurry into an electrochemical cell, wherein (i) the electrochemical cell comprises (A) a cathode in a cathode compartment and (B) an anode in an anode compartment, and (ii) the slurry is flown through the anode compartment; (c) providing a medium selected from a group consisting of (i) an electrolyte, wherein (A) the electrolyte is flowable though the cathode of the electrochemical cell, and (B) the electrochemical cell further comprises a membrane or separator between the anode and the cathode; and (ii) protons that can be pumped from decomposition of the plastic particles in the slurry from the anode and reduced at the cathode; (d) providing a voltage or current between the anode and the cathode of the electrochemical cell; and (e) oxidizing the plastic particles in the slurry to prepare a product selected from a group consisting of fuels, chemicals, oxy-hydrogenated products, and combinations thereof.
 2. The method of claim 1, wherein the product is selected from a group consisting of pure hydrogen, gasolines, monomers, and combinations thereof.
 3. The method of claim 1, wherein the product is an oxygen hydrogenated compound that can be used for at least of one the synthesis of materials and biochemical/thermal degradation.
 4. The method of claim 1, wherein the slurry is a mixture of plastics and polymers.
 5. The method of claim 1, wherein the slurry is formed by grinding plastics.
 6. The method of claim 5, wherein the slurry further comprises the electrolyte.
 7. The method of claim 1, wherein particle size of the plastic particles is in a range of about 10 microns and about 2000 microns.
 8. The method of claim 1, wherein the anode comprises a conductive material support selected from a group consisting of Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys, graphite, nickel foam, Ti foam, aluminum, aluminum foam, and combinations thereof.
 9. The method of claim 1, wherein the anode comprises a conductive material support selected from a group consisting of carbon, carbon fibers, and graphene.
 10. The method of claim 1, wherein the anode comprises a catalyst comprising a metal selected from a group consisting of Ni, Fe, Co, Cr, Mo, Pt, Rh, Ru, Pd, Ir, and combinations thereof, and composites of graphene metal combinations.
 11. The method of claim 10, wherein loading of the catalyst is in a range between 0.1 mg/cm² and 2 mg/cm².
 12. The method of claim 1, wherein the anode comprises a catalyst comprising carbon material selected from a group consisting of carbon fibers, carbon paper, carbon cloth, graphene, and carbon nanotubes.
 13. The method of claim 1, wherein the anode is a carbon fiber electrode comprising a Pt electrocatalyst.
 14. The method of claim 1, wherein the anode is a Ni mesh electrode.
 15. The method of claim 1, wherein the cathode comprises a conductive material support selected from a group consisting of Ni gauze/mesh, Ti, stainless steel, Ni—Cr—MO alloys, graphite, nickel foam, Ti foam, aluminum, aluminum foam, and combination thereof.
 16. The method of claim 1, wherein the cathode comprises a conductive material support selected from a group consisting of carbon, carbon fibers, carbon paper, carbon cloth, and graphene.
 17. The method of claim 1, wherein the cathode comprises an electrocatalyst comprising a material selected from a group consisting of carbon, graphene, Ni, Fe, Co, Mo, Pt, Rh, Ru, Pd, Ir, and combinations thereof.
 18. The method of claim 1, wherein the electrochemical cell comprises the electrolyte.
 19. The method of claim 18, wherein the electrochemical cell comprises the membrane.
 20. The method of claim 19, wherein the membrane comprises nafion or fritted glass.
 21. The method of claim 18, wherein the electrochemical cell comprises the separator.
 22. The method of claim 21, wherein the separator comprises polyethylene.
 23. The method of claim 18, wherein the electrolyte comprises an acid.
 24. The method of claim 23, wherein the acid is sulfuric acid or phosphoric acid.
 25. The method of claim 23, wherein the acid is at a concentration in a range of 0.1 M and 9 M.
 26. The method of claim 18, wherein the electrolyte comprises a catalytic additive.
 27. The method of claim 26, wherein the catalytic additive comprises an additive selected from a group consisting of Fe⁺², Fe⁺³, Cr⁺², Cr⁺³, V⁺³, V⁺², and salts thereof.
 28. The method of claim 26, wherein the catalytic additive is at a concentration in a range of 10 mM and 1000 mM.
 29. The method of claim 1, wherein the electrochemical cell comprises an additive.
 30. The method of claim 1, wherein the electrochemical cell further comprises a reference electrode.
 31. The method of claim 30, wherein the reference electrode comprises a material selected from a group consisting of Pt, Ni, Au, Ag/AgCl, Ag, and combinations thereof.
 32. The method of claim 1, wherein the step of oxidizing the plastic particles occurs while controlling temperature in a range between 20° C. and 180° C. 33-90. (canceled) 